Internet Engineering Task Force (IETF) M. Boucadair

Internet Engineering Task Force (IETF) M. Boucadair
Request for Comments: 8115 Orange
Category: Standards Track J. Qin
ISSN: 2070-1721 Cisco
T. Tsou
Philips Lighting
X. Deng
The University of New South Wales
March 2017

DHCPv6 Option for IPv4-Embedded Multicast and Unicast IPv6 Prefixes

Abstract

This document defines a Dynamic Host Configuration Protocol version 6
(DHCPv6) Option for multicast IPv4 service continuity solutions,
which is used to carry the IPv6 prefixes to be used to build unicast
and multicast IPv4-embedded IPv6 addresses.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8115.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. OPTION_V6_PREFIX64 DHCPv6 Option . . . . . . . . . . . . . . 3
4. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Configuration Recommendations for DHCP Servers . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9

1. Introduction

Several solutions (e.g., [RFC8114]) are proposed for the delivery of
multicast services in the context of transition to IPv6. Even if
these solutions may have different applicable use cases, they all use
specific IPv6 addresses that embed IPv4 addresses, for both multicast
group and source addresses.

This document defines a DHCPv6 option [RFC3315] that carries the IPv6
prefixes to be used for constructing these IPv4-embedded IPv6
addresses.

In particular, this option can be used in the context of Dual-Stack
Lite (DS-Lite) [RFC6333], Stateless Address plus Port (A+P)
[RFC6346], and other IPv4-IPv6 transition techniques.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2. Terminology

This document makes use of the following terms:

IPv4-embedded IPv6 address: an IPv6 address that embeds a 32-bit-
encoded IPv4 address [RFC6052]. An IPv4-embedded IPv6 address can
be a unicast or a multicast address.

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Prefix64: an IPv6 prefix used for synthesizing IPv4-embedded IPv6
addresses. A Prefix64 can be unicast or multicast.

Note: "64" is used as an abbreviation for IPv6-IPv4
interconnection.

ASM_mPrefix64: a multicast Prefix64 that belongs to the Any-Source
Multicast (ASM) range.

SSM_mPrefix64: a multicast Prefix64 which belongs to the Source-
Specific Multicast (SSM) [RFC4607] range.

uPrefix64: a unicast Prefix64 for building the IPv4-embedded IPv6
addresses of multicast sources in SSM mode.

3. OPTION_V6_PREFIX64 DHCPv6 Option

OPTION_V6_PREFIX64 (Figure 1) conveys the IPv6 prefix(es) to be used
(e.g., by an mB4 [RFC8114]) to synthesize IPv4-embedded IPv6
addresses.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_V6_PREFIX64 | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| asm-length | |
+-+-+-+-+-+-+-+-+ :
: ASM_mPrefix64 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ssm-length | |
+-+-+-+-+-+-+-+-+ :
: SSM_mPrefix64 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unicast-length| |
+-+-+-+-+-+-+-+-+ :
: uPrefix64 (Variable) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Option Format for OPTION_V6_PREFIX64

The fields of the option shown in Figure 1 are as follows:

option-code: OPTION_V6_PREFIX64 (see Section 6).

option-length: length of the option, in octets.

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asm-length: the prefix length for the ASM IPv4-embedded prefix, as
an 8-bit unsigned integer. This field represents the number of
valid leading bits in the prefix. This field MUST be set to 96.

ASM_mPrefix64: this field identifies the IPv6 multicast prefix to be
used to synthesize the IPv4-embedded IPv6 addresses of the
multicast groups in the ASM mode. The conveyed multicast IPv6
prefix MUST belong to the ASM range.

ssm-length: the prefix length for the SSM IPv4-embedded prefix, as
an 8-bit unsigned integer. This field represents the number of
valid leading bits in the prefix. This field MUST be set to 96.

SSM_mPrefix64: this field identifies the IPv6 multicast prefix to be
used to synthesize the IPv4-embedded IPv6 addresses of the
multicast groups in SSM mode. The conveyed multicast IPv6 prefix
MUST belong to the SSM range.

unicast-length: the prefix length for the IPv6 unicast prefix to be
used to synthesize the IPv4-embedded IPv6 addresses of the
multicast sources, as an 8-bit unsigned integer. As specified in
[RFC6052], the unicast-length MUST be one of 32, 40, 48, 56, 64,
or 96. This field represents the number of valid leading bits in
the prefix.

uPrefix64: this field identifies the IPv6 unicast prefix to be used
in SSM mode for constructing the IPv4-embedded IPv6 addresses
representing the IPv4 multicast sources in the IPv6 domain.
uPrefix64 may also be used to extract the IPv4 address from the
received multicast data flows. It is a variable-size field with
the length of the field defined by the unicast-length field and is
rounded up to the nearest octet boundary. In this case, any
additional padding bits must be zeroed. The address mapping MUST
follow the guidelines documented in [RFC6052].

Multiple instances of OPTION_V6_PREFIX64 may be returned to a DHCPv6
client. Configuration recommendations for DHCP servers are listed in
Appendix A.

Note that it was tempting to define three distinct DHCPv6 options,
but that approach was not adopted because it has a side effect: the
specification of a DHCPv6 option that could be used to discover
unicast Prefix64s in environments where multicast is not enabled.
Such a side effect conflicts with the recommendation to support the
Well-Known DNS Name heuristic discovery-based method for unicast-only
environments (Section 6 of [RFC7051]).

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4. DHCPv6 Client Behavior

To retrieve the IPv6 prefixes that will be used to synthesize unicast
and multicast IPv4-embedded IPv6 addresses, the DHCPv6 client MUST
include the OPTION_V6_PREFIX64 code in its OPTION_ORO. If the DHCPv6
client receives more than one OPTION_V6_PREFIX64 option from the
DHCPv6 server:

o If each enclosed IPv6 multicast prefix has a distinct scope
[RFC7346], the client MUST select the appropriate IPv6 multicast
prefix whose scope matches the IPv4 multicast address used to
synthesize an IPv4-embedded IPv6 multicast address.

o If at least two of the received options convey IPv6 multicast
prefixes that have the same scope, the said options MUST be
discarded.

If asm-length, ssm-length and unicast-length fields are all set to 0,
the DHCPv6 client MUST behave as if OPTION_V6_PREFIX64 had not been
received in the response received from the DHCPv6 server.

If the asm-length field is non-null, the IPv6 prefix identified by
ASM_mPrefix64 is used to synthesize IPv4-embedded IPv6 multicast
addresses in the ASM range. This is achieved by concatenating the
ASM_mPrefix64 and the IPv4 multicast address; the IPv4 multicast
address is inserted in the last 32 bits of the IPv4-embedded IPv6
multicast address.

If the ssm-length field is non-null, the IPv6 prefix identified by
SSM_mPrefix64 is used to synthesize IPv4-embedded IPv6 multicast
addresses in the SSM range. This is achieved by concatenating the
SSM_mPrefix64 and the IPv4 multicast address; the IPv4 multicast
address is inserted in the last 32 bits of the IPv4-embedded IPv6
multicast address.

If the unicast-length field is non-null, the IPv6 prefix identified
by uPrefix64 is used to synthesize IPv4-embedded IPv6 unicast
addresses as specified in [RFC6052].

5. Security Considerations

The security considerations documented in [RFC3315] and [RFC6052] are
to be considered.

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6. IANA Considerations

IANA has assigned the following option code in the "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)" registry
<http://www.iana.org/assignments/dhcpv6-parameters>:

Option Name Value
------------------ -----
OPTION_V6_PREFIX64 113

7. References

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.

[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<http://www.rfc-editor.org/info/rfc4607>.

[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010,
<http://www.rfc-editor.org/info/rfc6052>.

7.2. Informative References

[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, DOI 10.17487/RFC2365, July 1998,
<http://www.rfc-editor.org/info/rfc2365>.

[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
<http://www.rfc-editor.org/info/rfc6333>.

[RFC6346] Bush, R., Ed., "The Address plus Port (A+P) Approach to
the IPv4 Address Shortage", RFC 6346,
DOI 10.17487/RFC6346, August 2011,
<http://www.rfc-editor.org/info/rfc6346>.

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[RFC7051] Korhonen, J., Ed. and T. Savolainen, Ed., "Analysis of
Solution Proposals for Hosts to Learn NAT64 Prefix",
RFC 7051, DOI 10.17487/RFC7051, November 2013,
<http://www.rfc-editor.org/info/rfc7051>.

[RFC7346] Droms, R., "IPv6 Multicast Address Scopes", RFC 7346,
DOI 10.17487/RFC7346, August 2014,
<http://www.rfc-editor.org/info/rfc7346>.

[RFC8114] Boucadair, M., Qin, C., Jacquenet, C., Lee, Y., and Q.
Wang, "Delivery of IPv4 Multicast Services to IPv4 Clients
over an IPv6 Multicast Network", RFC 8114,
DOI 10.17487/RFC8114, March 2017,
<http://www.rfc-editor.org/info/rfc8114>.

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Appendix A. Configuration Recommendations for DHCP Servers

This appendix details a set of non-normative configuration
recommendations:

o DHCP servers supporting OPTION_V6_PREFIX64 must be configured with
ASM_mPrefix64 or SSM_mPrefix64, and may be configured with both.

o uPrefix64 must also be configured when SSM_mPrefix64 is provided.

o uPrefix64 may be configured when ASM_mPrefix64 is provided.

Note that uPrefix64 is not mandatory for the ASM case if, for
example, a local address mapping algorithm is supported or the
Well-Known Prefix (64:ff9b::/96) is used.

o Both ASM_mPrefix64 and SSM_mPrefix64 may be configured and
therefore be returned to a requesting DHCP client in the same
OPTION_V6_PREFIX64. In particular, if both SSM and ASM modes are
supported, ASM_mPrefix64 and SSM_mPrefix64 prefixes must be
configured. For SSM deployments, both SSM_mPrefix64 and uPrefix64
must be configured.

o When a multicast Prefix64 (ASM_mPrefix64 or SSM_mPrefix64) is
configured, the length of the prefix must be /96.

o When distinct IPv6 multicast address scopes [RFC7346] are required
to preserve the scope when translating IPv4 multicast addresses
(Section 8 of [RFC2365]), each scope is configured as a separate
OPTION_V6_PREFIX64. How DHCP servers are configured to separate
multicast Prefix64 per scope is implementation specific and not
covered by this document.

o When scope preservation is not required, only one instance of
OPTION_V6_PREFIX64 is configured.

Acknowledgments

Thanks to C. Jacquenet, S. Venaas, B. Volz, T. Taylor, R. Weber,
R. Even, J. Sheng, T. Mrugalski, and T. Chown for their review.

Many thanks to I. Farrer and T. Lemon for the comments.

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Authors' Addresses

Mohamed Boucadair
Orange
Rennes 35000
France

Email: [email protected]

Jacni Qin
Cisco
Shanghai
China

Email: [email protected]

Tina Tsou
Philips Lighting
United States of America

Email: [email protected]

Xiaohong Deng
The University of New South Wales
Sydney NSW 2052
Australia

Email: [email protected]

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